1. Field of the Invention
This invention relates to surgical instruments of the type which employs ultrasonic energy for operating on tissue and more particularly to an improved operative probe for use on such instruments to remove tissue from within a body and to the method of removing tissue from a body by use of such improved instruments.
2. Description of the Prior Art
Surgical instruments utilizing ultrasonic vibrations in combination with the circulation of irrigation liquid over the operative site for the removal of tissue from a biological body are well known and widely used particularly in enclosed or substantially enclosed operative sites. Such surgical instruments are particularly well adapted for use in the removal of cataracts and specific reference to such use will be made herein although it should be understood that the surgical instruments may be used for various other operative procedures.
The known ultrasonic surgical instruments of the type with which the present invention is concerned are frequently referred to as ultrasonic aspirators and conventionally employ an elongated probe or operative tip having one end rigidly attached through a vibration transmission member to a transducer for supplying ultrasonic energy to the other or free end of the probe where the ultrasonic energy is emitted to dislodge and break up or emulsify tissue for removal by aspiration. Irrigating fluid is delivered through a shield, or sheath surrounding the body of the probe for discharge adjacent to the tip or free end of the probe and returned by suction through the hollow center of the tubular body of the probe. An ultrasonic surgical aspirator of this type is disclosed in U.S. Pat. No. 3,805,787 and includes conduits for applying suction through the center of the vibration transmitting operative probe and for supplying irrigating fluid around the outer surface of the probe through a passage defined by a tubular shield. The irrigation fluid flows around the free end of the probe element and back through the center of the probe to effectively irrigate and remove dislodged and emulsified tissue. Various shield arrangements for controlling or directing the flow or irrigating fluid in the vicinity of the free end of the operative probe may be provided in accordance with this prior patent, and U.S. Pat. No. 3,693,316 discloses a flow control system for avoiding the application of excessive pressure or suction at the operative site.
The known ultrasonic aspirators have employed an elongated tubular vibration transmitting body having means such as an enlarged threaded head at one end for mounting the operative probe. The tubular body portion of the known probes have been circular in cross section and may be either cylindrical or slightly tapered from the mounting head to the operative tip. While such operative probes have been widely used, they are not entirely satisfactory for certain surgical procedures. For example, in removing a cataract lens from the eye it is necessary for the surgeon to make a small incision near the edge of the cornea to insert the operative probe and surrounding sheath into the eye to engage and emulsify the cataract lens with the distal end of the probe. Operative probes used for this purpose generally are tapered very slightly toward its distal or operative tip where the diameter may be approximately 0.043 and the end beveled, i.e., have an end surface in a plane which is inclined with respect to the longitudinal axis of the body. Depending on the physician's preference, the angle of the end bevel may vary, with 15, 30 and 45 degree bevels being commercially produced.
Inserting a round probe and sheath through the thin wound in the cornea spreads the margins of the wound and tends to induce wound gap which permits fluid leakage from within the eye. Stretching the wound also results in tighter contact between the cornea and the sheath surface and it is believed this tight contact may be a factor in inducing corneal burns which sometimes occur during eye surgery with these instruments.
Use of a round, beveled probe to sculp nuclear material from the anterior surfaces of the lens nucleus results in the material being removed in shallow furrows. The width of the furrows, and consequently the volume of aspirated nucleus, is limited by the diameter of the probe. Increasing the diameter of the probe would produce a corresponding increase in the furrow width but for various reasons it is desirable to maintain the size of the probe as small as is practical.